Portable speaker problems. ( First Post )

[GamingAddict]

Hello, as i just registered, and im building a portable speaker with salvaged 18650 batteries, i wanted to make a thread, cause i need to ask one thing. I have a problem. The amplifier for the speakers needs 12v, but as some of you may know, 1 18650 cell produces around 4 volts ar full charge, ive got 12 of these batteries, so ill take 4 and step the voltage down to 12. But the real problem is, i want to charge them with 5v cause i dont have a dedicated charger ( This charger circuit was salvaged from those portable power banks, in this case, it had only 1 cell in it ). The conclusion - I need 12v for the speaker, but i want to charge these batteries with a circuit from a portable power bank that can only charge 1 cell ( Or multiple if theyre in paralell ). Could someone tell me how could i do this ? Or even provide a 'cheap' circuit diagram ?

 

[sundy]

You will need to make a parallel circuit for charging and a series circuit for running your speakers. Or make a connection for each battery to charge and only connect the batteries in series for play back. They make connectors that break the circuit when plugged in.

 

[GamingAddict]

Hmm, thats a good idea, i kinda had the same, but i wasnt sure if its going to work.

 

[Audioguru]

Do you know that an 18650 cell is Lithium that is very dangerous? It is destroyed and might explode if you try to charge one that had its voltage drop below 3.0V so you must have a circuit to measure the battery voltage and disconnect it when its voltage drops below 3.0V per cell. The charger circuit from a Power bank will take a long time to charge 4 cells in parallel.

 

[GamingAddict]

I started thinking about that too... And about dropping below 3v, wasnt the case for me, i have built another portable speaker with an amplifier from a smaller one ( Basically, took the amp and charging circuit out of a smaller speaker and paired it with a bigger box, bigger speaker and bigger batteries ), the batteries i used for that were below 1.5v and theyre running great now, the speaker can play music for more than an entire day.

 

[GamingAddict]

I Just salvaged 6 more batteries from my friends laptop that died not so long ago. Maybe they still got some juice in them so i can charge them properly and use those, but im still going to need somekind of a protection circuit. Another option is - use those voltage step up boards, or whatever they are called. The 12v speakers amplifier doesnt use much, i could power it with a 12v 1.5a adapter, and it had no problems.

 

[Audioguru]

12V at 1.5A is 18W. The amplifiers might be class-AB with 55% efficiency then the maximum output power is 9.9W or the amplifiers might be class-D with 90% efficiency then the maximum output power is 16.2W.

Amplifiers are never always at full blast, their average power is about 1/10th so the average current is fairly low and a battery will last a long time.

 

[GamingAddict]

For the first speaker, it cant even max out a 5w 'subwoofer'

 

[Audioguru]

For the first speaker, it cant even max out a 5w 'subwoofer'

If the speaker impedance is 8 ohms and the amplifier has one output wire and one ground wire then the power when the output is barely clipping is about 1W.
If the speaker is 4 ohms and the amplifier is bridged with two output wires then the output power is about 7W.
If the speaker is 2 ohms and the amplifier is bridged with two output wires and has boostrapping then the output power is 30W.

Please post the schematic of your power amplifier so we can see which type it is.